The rotary filter disc continues to gain popularity as an efficient and cost effective approach to treating water. Such rotary filter discs have a relatively small footprint and are especially effective for tertiary filtration, water reuse, and solids removal.
Typically rotary filter discs include a rotary drum having a plurality of axially spaced rotary filter discs mounted on that drum. Influent water or wastewater is fed into the drum and from the drum the water or wastewater passes into the interior of the rotary filter disc. Each rotary filtered disc includes opposite side walls made up of filters. An inside-out flow pattern is utilized and the influent water or wastewater in the interior of the rotary filtered disc moves outwardly through the filters to produce a filtered effluent that is collected in a collection tank. From the collection tank, the filtered influent can be directed to other downstream processes or discharged in various ways.
Over time solids accumulate on the inside surfaces of the filters. A backwashing subsystem is provided on the rotary filter disc for periodically cleaning the filters. More particularly, periodically the rotary filter discs are rotated and after portions of the filter have emerged from the effluent collection tank, nozzles spray a cleaning solution on the outer side of the filters causing the solids and other debris located on the inner surfaces of the filter to fall into a trough or collection area, after which they are removed from the rotary filter disc.
Over time, because of the repeated accumulation of solids on the inner surfaces of the filters followed by cleaning, the permeability of the filters vary. Furthermore, the flow of influent water to the rotary filter disc can also vary. These variations can cause surges in the flow of effluent produced by the rotary filter disc. For example, assume that the filters gather significant solids and debris on the inner surfaces, and that this substantially reduces effluent flow from the rotary filter disc. This in turn causes the influent water to back up. Then, for example, the filters of the rotary filter disc are cleaned quickly. This results in a substantial increase in flow through the filters, producing downstream flow surges in the effluent. As noted above, this can make it difficult to effectively and efficiently perform downstream treatment operations.
Therefore, there is a need for a control approach that utilizes a variety of actions with respect to rotating the rotary filter discs and backwashing so as to conserve energy and at the same time dampen the surges normally associated with effluent flow from a rotary filter disc.